TOTAL SEDIMENT BIOMASS AND PRELIMINARY ESTIMATES OF ORGANIC-CARBON RESIDENCE TIME IN DEEP-SEA BENTHOS

Estimates of 'total' biomass of the benthos (bacteria, meiofauna, macrofauna) in terms of organic carbon have been assembled for 9 stations over a broad water-depth range in the western North Atlantic. The largest size category, the macrofauna, was dominant in sandy continental shelf sediments, whereas the smaller forms (bacteria and meiofauna) dominated at greater depths. Biomass of the 'total' benthos and of each size category correlated much better with POC flux than with sediment detrital organic carbon, reinforcing the idea that most organic matter is consumed on the sediment surface, rather than within the sediments. An overall increase in the relative importance of smaller size categories of organisms with increasing depth supports the idea that the importance of bacteria (in remobilizing recalcitrant organic compounds) increases with depth, reaching a maximum at great depths far offshore. The 'average' residence times for both the living and the detrital organic carbon stocks at various depths were calculated by dividing the 'estimated (organic carbon) remineralization' rate (POC flux estimated with sediment traps minus long-term burial) into both the biomass and sediment detrital organic carbon concentrations (corrected for living biomass). The biomass appeared to turn over on average time scales of months, whereas the total detrital sediment organic matter appeared to turn over on scales of years to centuries, depending on depth and sediment type.